You may be able to get a thinwall sleeve from a bearing supplier for the needle roller to run on. I fitted one on a motorcycle gearbox shaft to repair it.

https://simplybearings.co.uk/shop/Bearings-Needle-Roller-Bearings-Needle-Roller-Inner-Rings/c3_29_35/index.html

Edited By old mart on 27/07/2021 17:12:53

If the shaft bis soft, it is possible that the rollers will brinell the shaft, when subjected to a repeated cyclic load.

In one instance the ratio between shaft diameter and roller diameter meant that the cyclic load was applied in almost exactly the same point every time.. The shaft suffered, and the design had to be altered.

Howard

Duncan, you can turn and face the hardened rods using carbide cutters. I used linear bearings when making the guide for the z axis DRO fitted to my Chester Super Lux milling machine. The swarf gets hot!, but given the small diameter shouldn't be a problem. The supplier advised the shaft was only surface hardened but on 8mm dia. in fact seemed to extend throughout the rod.

Robert Butler

You could look at sintered bronze bearings, available in metric and imperial, self lubricating and already made to size.

I think you will need to do everything you can to minimise friction, so plain bushes may not be the best idea. On the other hand. I very much doubt that the loads and speeds from a hot air engine would require hardened shafts if you wanted to stick to the original design.

You may actually be better off machining the main bearings. Oilite etc are a bit oversize until pressed into a hole and you may not be able to close them down with the separate bearing caps and end up with a loose fit unless you turn the crankshaft to fit from larger dia stock